measurements of light output are generally accurate since they The absolute light outputs of BGO, CsI(T1) and some new Ce-doped crystals have been measured to an accuracy of about 55 % using calibrated XP2020Q photomultipliers and standard S3590-03 and S2740-03 photodiodes. The use of small crystals, 9 mm in diameter and 1 mm thick, reduces the corrections for imperfections in the light collection process and in the photoelectron collection by the photomultipliers. The measured light output of 8500k350 ph/MeV (photons/MeV) for the BGO crystals agrees well with the earlier measurement done by Holl et al. The carried out study highlighted the importance of the spread in the published emission spectra of the crystals which seems to limit measurement accuracy. Finally, a simple comparative method of measuring light output to an accuracy of +.lo %, is proposed using an uncalibrated XP2020 photomultiplier and a 1 mm thick BGO crystal as a standard.

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Three pure NaI crystals grown in different batches by Scionix (Holland) were studied at room and liquid nitrogen temperatures. The room temperature studies performed with photomultiplier readout covered measurements of emission spectra, photoelectrons yield and energy resolution. Moreover, the scintillation light pulses were measured by single photon method. Two crystals showed the photoelectron yield of about 1000 phe/MeV measured at room temperature with an XP2020Q photomultiplier. The energy resolution of the 662 keV photopeak was measured to be about 16% and was limited mainly by a low number of photoelectrons and a large non-proportionality of the light yield. The fast light pulse had the main decay time components of 1 ns and 5 ns. The high initial photon intensity of the tested NaI crystals revealed in the good timing resolution of about 140 ps obtained for 60 Co γ γ γ γ-rays. At liquid nitrogen temperatures the measurements of light yield and energy resolution were performed using Advanced Photonix, Inc. avalanche photodiode readout. A high light output above 80000 ph/MeV was measured for the best of the tested crystals. The energy resolutions of the 662 keV photopeak of the three crystals differ a lot, varying from an excellent value of 3.8 % to 6.2 %. This suggests that the measured energy resolutions depend on the purity of the scintillator samples reflected in the emission spectra. The studies that were performed demonstrate the attractive properties of pure NaI at both room and LN 2 temperature.

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